Isolating Micro-Machined Accelerometer Zero-G Bias Shifts under Static Thermal Cycles
Static thermal zero-g bias shifts in MEMS accelerometers are isolated by enforcing prolonged thermal dwell periods to decouple stress creep from thermal gradients.
PCB Laminate Slotting
Fabrication Technique
Cutting narrow openings through a printed circuit board substrate is used to increase electrical isolation and reduce mechanical stress between different sections of the assembly. This process, referred to as PCB laminate slotting, prevents high-voltage leakage along the board surface and isolates delicate analog circuits from the thermal expansion of power components. The physical gaps create an air barrier that has a much higher dielectric strength than the glass-epoxy composite material.
This barrier is crucial for protecting low-voltage sensors from high-voltage transients on the same board.
Machining Specification
Creating these gaps requires the use of specialized routing bits and precise drill paths during the board fabrication process. The minimum width of the slot is determined by the diameter of the routing tool, which is typically between zero point eight and two millimeters. This dimension must be carefully balanced with the thickness of the laminate to prevent the board from warping or breaking during assembly.
These routing paths are defined in the Gerber files of the board design, which guide the automated milling machine.
Isolation Verification
Testing the effectiveness of the slots involves high-voltage isolation measurements performed under controlled humidity conditions to simulate harsh environments. A high-voltage tester applies a potential across the slot and measures the leakage current, which must remain below a specified threshold. This verification is essential for boards used in industrial or automotive applications where moisture and dust can accumulate on the surface and create conductive paths.
This testing ensures that the slot provides the required level of protection over the lifetime of the product.
Mechanical Constraint
Surface mount components must be positioned a minimum distance away from the edges of the slot to prevent mechanical stress from cracking the solder joints. When the board is handled or subjected to temperature changes, the areas near the slots experience localized bending that can damage fragile ceramic capacitors and resistors.